Primarily, the present invention relates to centering a gem stone, e.g. so that a rough stone can be worked by a process which involves rotating the stone about an axis.
The working which is being primarily considered is bruting, which is the procedure of cutting or grinding a girdle on the rough stone, after the stone has been sawn (the sawn rough stone is called a "sawn-half"). However, the working could for instance be coning, which is forming a cone on the culet or table side of the sawn half.
Particularly referring to bruting, the present procedure in general is to brut, block at a culet half angle slightly greater than the desired angle to determine the position of the culet point, re-brut, and final block at the desired culet half angle. For a standard shape diamond, the first block would be at a 43.degree. half angle and the second block at at 41.degree. half angle.
In the art, the support which is used to support a gemstone while it is being worked is normally referred to as a "drop". In general terms, the support can have any suitable size or shape.